A pair of hearing-aids can range in cost from $1800 to $6,800 and generally last 4-6 years. The cost of ownership including batteries and maintenance can add further expense over the hearing-aid's lifetime. For many Americans with HL, hearing-aids can be the 3rd most expensive item, after their home and car. The hearing-aid device itself is relatively inexpensive to manufacture, but typical fitting procedures add expense and inconvenience.
Despite expert efforts at fitting and adjustment, many users are unsatisfied with device performance at various times during real-world use of a device. User satisfaction is affected by speech quality, clarity of sound, natural sound, richness/fidelity of sound, comfort with loud sounds, and sound of own voice (occlusion). While recent advances have made fewer hearing-aids end up “in the drawer”, there remains a small percentage of patients who are “satisfied” or “very satisfied”. Reasons for this level of dissatisfaction have been identified for more than a decade. See, Kochkin, S., “MarkeTrak V: ‘Why my hearing-aids are in the drawer’: The consumers' perspective, The Hearing Journal, Vol. 55, No. 2 pp. 34-41 (February 2000). Kochkin's report identified the poor performance of hearing-aids in providing clarity in noisy environments as being a primary factor for the hearing-aids to end up “in the drawer,” i.e., not used. The user determines that too little benefit is provided to warrant use of the hearing-aid. The solution proposed in the Kochkin article to address the clarity issue included multiple-microphone hearing-aids that allow the user to choose between omnidirectional and unidirectional modes.
The basic problem is that a hearing-aid's output is being received by a damaged inner ear. A consequence of the damage is that noise has a greater effect on speech perception than it does for undamaged ears. Some prior solutions include use of a wireless microphone for the talker of interest (highly effective, but impractical). directional (or beam-forming) microphones aimed at the talker of interest (somewhat effective but less so in many real-world environments where the directional sound is less important than reflected sounds), and noise “reduction” (effective in reducing perceived “noisiness” and reducing listening effort but not in improving speech recognition).
FIGS. 1A and 1B respectively illustrate the left and right hearing-aid components of a conventional modern hearing-aid. The power amplifier (PA) and pre-amp are analog components. A speaker provides a signal to the PA, which is then converted by an analog to digital converters (ADC) and then processed by a digital signal processor (DSP). The DSP processes the signal to enhance clarity and filter noise. A conditioned signal is output and converted by a digital to analog converter (DAC). The analog output is amplified and an auditory signal is output by a speaker. Typical current consumption is about 1 mA, with 700 μA for the DSP. The analog to digital convertor (ADC) and the digital to analog convertor (DAC) typically operate at 16 kHz sampling, providing at most 8 kHz bandwidth for the audio path. There is negligible speech information at frequencies above 8 kHz. However, people with normal hearing may benefit in terms of sound quality and perceiving sound direction and localization with signals that extend above that range. Some emerging hearing-aids provide digital wireless transmission using radios such as Bluetooth. These wireless links support speech and audio path to off-body devices such as smartphones, but compensation is still implemented on the local DSP with limited power budget. Radios such as Bluetooth support multiple applications and consequently are not “power” optimized for hearing-aid functionalities. The current consumption of state-of-the art radios can be as high as 10 mA.
Noise suppression is also of interest to users having normal hearing. For example, hearing protection is worn by users in various environments, such as military and industrial environments. A standard approach is to wear protection that attenuates all acoustic sources. Such users could benefit from selective noise suppression.